powerpc/tools: Remove 90 line limit in checkpatch script

As of commit bdc48fa11e46, scripts/checkpatch.pl now has a default line
length warning of 100 characters. The powerpc wrapper script was using
a length of 90 instead of 80 in order to make checkpatch less
restrictive, but now it's making it more restrictive instead.

I think it makes sense to just use the default value now.

Signed-off-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200828020542.393022-1-ruscur@russell.cc

powerpc/tools/checkpatch: Ignore DT_SPLIT_BINDING_PATCH

From what I've seen, every time this warning comes up it's bogus,
so let's ignore it.

Signed-off-by: Russell Currey <ruscur@russell.cc>
Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

powerpc: Add a checkpatch wrapper with our preferred settings

This makes it easy to run checkpatch with settings that I like.

Usage is eg:

$ ./arch/powerpc/tools/checkpatch.sh -g origin/master..

To check all commits since origin/master.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Russell Currey <ruscur@russell.cc>